Definition:&nbsp Elements such as silicon and aluminium when added to molten steel react to form stable oxides and reduce the amount of dissolved oxygen. The solubility of oxygen in steel is reduced as temperature is lowered during solidification and the excess oxygen combines to form carbon monoxide. If the molten metal is not deoxidised the effervescence produced by the evolution of carbon monoxide during solidification would result in blow holes and porosity. Steel treated in this way is termed, "Killed Steel".